Process and apparatus for mining deposits on the sea floor



July 22, 1969 j GRAHAM ET AL 3,456,371

PROCESS AND APPARATUS FOR MINING DEPOSITS ON THE SEA FLOOR Filed May 6,1965 6 SheetsSheet 1 F/G./. F/G.8.

5 MOVEMENT OI SHIP DIRECTION OF UREDGING July 22, 1969 J. R. GRAHAM ETAL 3,456,371

PROCESS AND APPARATUS FOR MINING DEPOSITS ON THE SEA FLOOR Filed May 6,1965 6 Sheets-5heet 2 July 22, 1969 J, GRAHAM ET AL 3,456,371

PROCESS AND APPARATUS FOR MINING DEPOSITS ON THE SEA FLOOR- Filed May 6,1965 6 Sheets-Sheet S July 22, 1969 GRAHAM ET AL 3,456,371

PROCESS AND APPARATUS FOR MINING DEPOSITS ON THE SEA FLOOR Filed May 6,1965 6 Sheets-Sheet 4 F/G.5. F/GZ July 22, 1969 J. R. GRAHAM ET AL3,456,371

PROCESS AND APPARATUS FOR MINING DEPOSITS UN Till-i SEA FLOOR Filed May6, 1965 6 Sheets-Sheet b FIG.

2" WIRE PIPE LlNE case PENDENT s'rRucwxE PIPE A \l I \IG l July 22, 1969G M ET AL 3,456,371

PROCESS AND APPARATUS FOR MINING DEPOSITS ON THE SEA FLOOR Filed May 6,1965 6 Sheets-Sheet 6 .rzmozmu m2: UNIS of uni maowxn don xufim UnitedStates Patent M 3,456,371 PROCESS AND APPARATUS FOR MINING DEPOSITS ONTHE SEA FLOOR John R. Graham, Newport Beach, and Algernon A. Mabson,Long Beach, Calif, assignors to Kennecott Copper Corporation Filed May6, 1965, Ser. No. 453,734 Int. Cl. E02f 1/00, 3/ 88, 3/90 U.S. Cl. 3719511 Claims ABSTRACT OF THE DISCLOSURE Deposits of manganese nodules andother minerals are found on the sea floor at depths of a thousand feetand greater. These nodules lie exposed on the sea floor, either directlyon the surface of the sea floor or buried. For example, the presence ofsuch nodules has been photographed on the floor of the North AmericanBasin, off the coast of Florida.

These nodules contain manganese and iron in substantial quantity, and inaddition, valuable amounts of copper, cobalt, nickel, and other metals.The nodules vary in size and shape. They tend to be spherical, and theirlargest dimension may be up to about eight inches or larger. Theeconomic recovery of these nodules poses several challenging problems.

One object of the present invention is to provide a new and practicalprocess for mining deposits on the sea floor. A related object of theinvention is to provide practical equipment for practicing this process.

A more specific object of the invention is to provide practicalprocesses and devices for the economic recovery of manganese nodulesfrom sea floor deposits.

Another object of the invention is to provide new and practicaltechniques for transporting liquid-solid mixtures upwardly from the seafloor, through relatively long lengths of dredge pipe.

A further object of the invention is to provide new and practicaltechniques for mining valuable deposits that are distributed on thesurface of the sea floor and that are embedded in the first few inchesor feet of the sea floor.

Still another object of the invention is to provide efficient, effectivetechniques and equipment for recovering manganese nodules from the seafloor, at costs that can be economically competitive considering thevalue of the recoverable minerals that are available in the nodules.

Other objects of the invention will be apparent hereinafter from thespecification and from the recital of the appended claims.

In the drawings:

FIGURE 1 is a fanciful, fragmentary view showing a surface vesselunderway on the surface of the sea, a gathering vehicle for movement onthe sea floor, and an articulated dredge pipe interconnecting thesurface vessel and the gathering vehicle, all in accordance with onepreferred embodiment of the present invention;

FIGURE 2 is a fragmentary side elevation on an enlarged scale, of thegathering vehicle on the sea floor,

3,456,371 Patented July 22, 1969 with the direction of movement of thevehicle being indicated by an arrow;

FIGURE 3 is atop plan view thereof;

FIGURE 4 is a fragmentary section taken on the line 44 of FIGURE 3,looking in the direction of the arrows;

FIGURE 5 is a fragmentary side elevation, partly broken away, of asection of the dredge pipe and an adjacent and connected section of acompressed air pipe, that communicates with a jacket about the dredgepipe for injecting air under pressure into the dredge pipe;

FIGURE 6 is a sction taken on the line 66 of FIG- URE 5, looking in thedirection of the arrows;

FIGURE 7 is a fragmentary part elevation, part section, of the receivingtank into which the dredge pipe discharges when an air lift is employedto transport the mined nodules mixed with sea water through the dredgeFIGURE 8 is a fragmentary part side elevation, part vertical section, onan enlarged scale, of different kinds of joints that are employedbetween adjacent sections of the dredge pipe;

FIGURE 9 is a side elevation of a pump, and of a cage in which it ismounted, for producing a hydraulic lift to transport mined materialupwardly through the dredge pipe, with the direction of flow indicatedby arrows;

FIGURE 10 is a fragmentary side elevation of a surface vessel forsupporting the dredge pipe and temporarily storing the mined nodules,and

FIGURE 11 is a fanciful elevation showing the gathering vehicle in aseries of different positions through which it would be moved whenhoisted from the sea floor up into the surface vessel, or vice versa.

Referring now in detail to the drawings by numerals of reference, thenumeral 14 denotes generally a gathering vehicle or tractor that isdesigned for movement over the floor of the sea. A surface vessel 15 isshown under way on the surface of the sea, in proximity to the positionof the tractor. A dredge pipe 16 is suspended from the vessel 15, and isbuoyed up by multiple buoyancy tanks 18 that are secured to the dredgepipe at intervals below the surface of the sea. The lower end of thedredge pipe forms, under its own weight, a shape that is referred toherein as a catenary 19, although it is recognized that drag and otherforces also act on this pipe, so that it is technically not a truecatenary. Several of the sections of the pipe are interconnected witheach other, in this catenary portion, by flexible ball joints 20. Asturdy line 21 is anchored at its lower end to the tractor 14, and isconnected at its upper end to a buoy 22 that is shown floating in closeproximity to the surface vessel 15.

THE TRACTOR The tractor 14 is designed and equipped to be remotelycontrolled from the surface vessel 15. Its function is to move over thesea floor, following a pattern of back and forth movement, and to skimnodules from the sea floor. Essentially, the tractor performs a stripmining operation.

Referring now particularly to FIGURES 2, 3 and 4, the tractor 14 isformed with a rugged metal frame that is, however, formed of a lightmetal such as, for example, aluminum, to keep the over-all weight low,so that the bearing pressure on the surface of the sea floor will beless than one pound per square inch. The frame includes a front crosstube 24, a rear cross tube 25, and a center bracing structure that isgenerally indicated by the numeral 26 (FIGURE 4), all three of whichinterconnect the two side beams 28. A pair of drive sprockets 29 aremounted at the opposite ends of the front cross tube 24.

Each of these drive sprockets 29 is connected through its own respectiveshafting 30 and gear train 31 to its own individual electric drive motor32. Each of these drive motors is individually mounted and rigidlysecured on its own platform 34, that is supported on cross braces 35that extend between the front cross tube 24 and the side beams 28, andbetween the side beams 28 and the center bracing structure 26,respectively. Each motor is independent of the other so that the tracks38 need not be operating at simultaneously equal speeds or in the samedirection.

A plurality of tires 36 are mounted along each side of the gatheringvehicle, and each tire is separately and individually suspended from oneof the side beams 28. A pair of crawler tracks 38 is mounted, one ateach side of the tractor, about the drive sprockets 29 and the tires 36.The tires 36 are preferably hollow and filled with liquid, to avoidcollapse at operating depths.

A heavy bumper 39 is secured to the front cross tube 24, and isproportioned to extend across the entire width of the front end of thetractor. The bumper 39 projects in advance of the tractor and protectsthe crawler tracks as well as the tractor body.

A pair of masts 40 are secured to the center brace 26, at opposite sidesof the tractor respectively. A cross beam 41 is secured between theupper ends of the masts 40, so that the masts 40 and cross beam 41together form a structure that is generally in the shape of an invertedU. An eye plate 42 is secured centrally on the cross beam 41, to facethe front of the vehicle, for a purpose to be described presently. Asimilar eye plate 44 is secured to the upper surface of the cross beam41, projecting upwardly, to provide anchorage for the pendent line 21.The apex of an A-shaped truss 45 is rigidly secured to the rear face ofthe cross beam 41 at its apex, and each of its legs is rigidly securedto opposite sides respectively of the rear cross tube 25.

Individually mounted heavy spring rake tines 46 are supported by a crossbeam 47. The lower, free ends of the rake tines are disposed to projecta short distance below the lower surfaces of the crawler tracks 38. Thisar- .rangement permits the tines to rake the surface of the sea floorand to deflect by swinging toward the rear and upwardly, uponencountering some unusually large or immovable obstruction.

A pair of scraper blades 49, 50, are each respectively secured to thecenter brace 26 of the vehicle frame for pivotal movement about verticalaxes by pins 51, 52, respectively. These pins interconnect the frame andthe outboard ends of a pair of frontally-disposed web portions 54, 55,that are integral with the scraper blades, respectively. These webportions 54, 55 are in turn pivotally secured by pins 53, 57,respectively, to the pistons of spring plungers 56, 58, repectively,that spring-press the scraper baldes to the diagonal position shown bestin FIG- URE 3, in which the two scraper blades converge together towardthe rear or trailing end of the tractor.

Several desirable accessory items for the tractor are not illustrated,in order to simplify the drawings. For example, the tractor should beprotected from damage by sonic or supersonic scanning of its immediatepath, and for this purpose, a forward searching sonar unit may bemounted on the tractor. It is also desirable to provide closed systemtelevision, with floodlights trained to illuminate the path. Theprovision of an inclinometer on the tractor, and of a pan and tiltdevice on the TV camera to permit inclinometer readings, also isdesirable. To operate underwater television successfully at depthsgreater than about 6,000 feet, it may be desirable to install amplifiersin the cable. Water-tight connectors are used for this purpose.

Each of the crawlers of the tractor preferably is independently drivenby its individual motor, as shown in the drawing. By way of example, fora tractor weighing about 20,000 pounds, and carrying none of the Weightof the dredge pipe, each crawler can be powered by a 75 H.P.submersible, two speed, reversible electric motor with a built-in gearreduction.

There motors may be supplied with three-phase AC. power at 4,000 volts,depending on depth. Suitable controls on the surface vessel are providedto start, stop and reverse the motors, and also to change speeds as maybe necessary. The tractor may be turned by slowing one of the crawlerunits, or by going forward on one crawler unit and to the rear on theother. The same electric power cable may provide power for a pump forjetting on the sea floor, in the path of the tractor.

THE DREDGE PIPE As is best shown in FIGURE 10, the surface vessel 15 isformed with an open center well 61. A pneumatic or hydraulic shockabsorber or shock plunger 62 is mounted within this well, and the upperend of the dredge pipe is secured to the shock plunger.

The dredge pipe is formed from sections that are preferably about eightyfeet long, and that are interconnected in the following manner. Over themain portion of the length of the dredge pipe, each of the pipe sections64 (FIGURE 8) is formed with a flange fitting 65 at each of its ends.The flange fittings of adjacent pipe sections are held together withclamp fittings 66, in watertight fashion.

In those portions of the pipe where flexibility is required, such as,for example, in the catenary portion 19 at the lower end of the pipe,ball joints are employed between adjacent pipe sections where required.One form of ball joint, that may be employed, consists of a femalefitting 68 that is welded or otherwise secured to one end of a pipesection. The confronting end of the adjacent pipe section is providedwith a mating male fitting 69, that can be received in substantiallywatertight engagement within the female fitting. A clamping collar 70 issecured to the end of the female fitting 68 by a plurality of pivotedbolts 71 that are secured in angularly spaced relation about the femalefitting. The collar 70 is proportioned to restrain the two fittings 68,69 against relative axial movement, While permitting relative rotarymovement, in a manner well known in the art.

Preferably, the individual sections of the dredge pipe are selected foroptimum strength and weight characteristics. For example, the lowersections of the dredge pipe, that are secured to the gathering vehicle,may be made of welded aluminum. The wall thicknesses of the pipesections may be progressively increased, from the sea floor upward, asneeded, to provide adequate strength for supporting the lower pipesections, and the upper sections of the dredge pipe may be formed fromhigh tensile welded steel, rather than from aluminum.

For long strings of dredge pipe, buoyancy tanks 18 or other buoyantitems or materials are secured to the dredge line, below the surface, toprovide support for a substantial part of the weight of the dredge pipe.

At its lower end, the last section 72 of the dredge pipe is operativelyconnected to the tractor in the following manner. An eye plate 74(FIGURE 2) is secured to the end of the pipe section 72 that is remotefrom the tractor, and a line 75 interconnects the eye plate 74 with aring 76 that is secured in the pendent line 21. A collar '78 is mountedintermediate the ends of the pipe section 72. This collar is formed witha pair of eyes, and one line 79 interconnects the collar 78 with thefrontfacing eye plate 42 on the cross beam 41 of the tractor, and asecond line 80 interconnects the collar with an eye bolt that is securedto the front cross tube 24.

The pipe section 72 is connected through an L fitting 84 with a flexibleball joint 85, that permits limited move ment of the dredge piperelative to the tractor. The ball joint 85 is mounted on an L 86 (FIGURE4) that is secured to the center brace 26 of the tractor by a cradle ofsupporting webs 88. The L 86 in turn is connected through a flexibleball joint 89 with a short stub pipe 90 on which the collector head 91is mounted.

The collector head 91 is formed with a lower face 92 that confronts thesea floor during normal mining operations. This lower face 92 is formedwith a large, generally rectangular opening, across which a heavy screenor grille 94 is mounted, to prevent the entrance of undesirably largearticles into the dredge pipe.

A pair of lugs 95 are secured to the opposite respective sides of thecollector head, adjacent its upper end. A pair of arms 96 are rigidlysecured to these lugs, and project toward the rear of the tractor. Thesearms 96 are formed, at their respective free ends, with massive, slottedguide members 98. The rear frame tube of the tractor is slidablyreceived within the slots of these guide members. A pair of stop rings97 are secured on the tube 25, on the outboard sides of the guidemembers 98 respectively, to limit movement of the guide memberslengthwise of the tube.

The two guide members 98 are rigidly interconnected together by atransverse heel member 99, that is disposed beneath the frame tube 25.The heel member 99 is formed with a rounded lower face, to ride on thesea floor, and with an upwardly curved central lip portion 100.

During movement of the tractor, the lower face of the heel 99 rides overthe sea floor, but when an irregularity is encountered, the heel 99 andthe guides 98 rise up or drop down, and as they do so, they cause thearms 96 to move correspondingly, carrying the collector head 91 up ordown with them.

In strings of dredge pipe over 9,000 feet long, at least two buoyancytanks are ordinarily used, each having a positive buoyancy of at leastabout 100,000 lbs. These tanks are provided with an initial internal airpressure of about 1,000 p.s.i., before being submerged, attached tosections of the dredge pipe.

If desired, a plurality of buoyancy tanks can be employed of smallerbuoyancy capacity than mentioned above. The use of a plurality of suchtanks produces a more uniform distribution of stress along the length ofthe dredge pipe and makes possible the use of less heavy and thereforeless strong dredge pipe sections and joints.

To provide for the catenary at the lower end of the dredge pipe, and toprovide flexibility and limited mobility for mining operations at adepth of about 6,000 feet, about 7,000 feet of pipe should be used; andfor operations at about 12,000 feet, about 13,500 feet of pipe should beused. For deeper operations, appropriate additional increments of pipeshould be provided.

THE AIR LIFT To transport mined material from the surface of the seafloor up through the dredge pipe, it is preferred to employ an air lift.This transporting technique utilizes an injection of compressed air intothe dredge pipe, at some distance below the sea surface and at somedistance above the sea floor, to form within the dredge pipe first a twophase mixture of air and sea water, and then, as operations begin, athree phase mixture of air, sea water, and dredged solid material. Thesemixtures are lighter than the sea water surrounding the dredge pipe, andthe pressure of the surrounding sea water forces the mixture up throughthe dredge pipe.

Referring now particularly to FIGURES 5 and 6, to provide for the airlift, a section 102 of relatively small diameter pipe is secured bystraps 104 to each section of dredge pipe, above the air injection site,to carry compressed air to the injection site. A quick-disconnectfitting 101 is secured to each end of each air pipe section. Thequick-disconnect fittings 101, at the end of each air section, areconnected to the confronting fittings of adjacent air pipe sectionsthrough short, flexible interconnecting flexible nipples 105.

At the air injection site, a special dredge pipe section 106 is providedwith an external jacket 108, intermediate its ends. The wall of thedredge pipe section 106, that is enclosed within the jacket 108, isformed with a plurality of perforations 109, to admit air from thejacket into the dredge pipe. A pair of curved pipes 110 interconnect andprovide communication between the lower end of the air pipe 102 and theinterior of the jacket 108.

For efficient operation of the air lift, the dredge pipe is mounted todischarge into a chamber at superatmospheric pressure. This chamber isprovided in a tank 111 (FIGURE 7) that is mounted on a movable base 112.A connecting pipe 114 is mounted to provide communication between theupper end of the dredge pipe, that is suspended from the shock plunger62, and the tank 111. A curved baifie 115 is mounted within the tankchamber, over the discharge opening of the connecting pipe 114, todeflect the stream that is injected into the tank chamber, and topreserve the tank against wear.

A rotary valve 116, at the bottom of the tank, permits continuousdischarge of nodules from the tank, during operations. A riser 118 isconnected to the tank chamber at its lower end, and is open to theatmosphere at its upper end. At different elevations, sliding gates orvalves (not shown) are connected to the pipe, to permit sea Water to runout of the pipe into one or more of several troughs 117, that aresecured to the pipe 118 in positions, respectively, to receive therunoff water. This arrangement facilities control over the head that ismaintained within the tank 111.

The tank 111 is maintained at superatmospheric pressure to avoid thepinch effect that would otherwise occur during air lift operations. Thepinch effect can be explained in the following manner. A bubble of airthat is rising, under generally isothermal conditions, through severalhundred feet of water to the surface, will expand to many times itsoriginal volume. For example, if the bubble rises 3400 feet, it willexpand to approximately 100 times its original volume. Moreover, 50percent of the total expansion will take place in the final 34 feet ofthe ascent, where the static head or back pressure is lowest. Such atremendous expansion, in the final section of the dredge pipe, couldtend to generate unfavorable conditions.

THE SURFACE VESSEL The surface vessel 15 is provided with a derrick 119that is mounted over the vessels center well 61, to facilitate handlingthe dredge pipe sections when raising and lowering, or simply changingthe length of, the dredge pipe. A crane 120 is mounted adjacent thederrick, for hoisting the pipe sections, and transporting them to andfrom the storage racks 121, or from supply vessels. An A-frame and boom122 are mounted at the front of the ship, for handling the pendent line21, when necessary. The pressurized discharge tank 111 is mountedadjacent the derrick 119 and the center well 61, to facilitateconnecting the dredge pipe for discharge.

The surface vessel is preferably equipped for dynamic positioning, thatmakes it possible for the surface vessel to maintain a substantiallyfixed position on the surface of the sea, for indefinite periods oftime, or to move in a predetermined path, as necessary.

HYDRO-LIFT Instead of using an air lift for transporting material up thedredge pipe, other transport systems can be em ployed. A preferredalternative makes use of at least one rotary pump, located in the dredgepipe, for developing enough lifting action to transport mined materialeffectively.

One form of pump, that may be employed in connection with such analternative embodiment of the invention, is illustrated in FIGURE 9. Thepump 125 is a centrifugal type rock pump having a non-clogging impeller,and is mounted in a particular section 126 of the dredge pipe 16. Thepump is provided with a pair of discharge pipes 128, that are parallelfor a short distance, to provide the inner part of a cage structureabout the enclosed submersible electric motor 129 that drives the pump.These discharge pipes are connected together above the motor, tocommunicate with a single section of the dredge pipe. Preferably, anouter cage structure 130 is provided, through which there is no flow,and whose purpose is to provide the supporting structure for the motorand pump, and also to maintain the tensile strength of the dredge pipe.

More than one pump may be used, as necessary, depending upon the depthof the Water at which mining is 10 taking place. If more than one pumpis used, the pumps are mounted and operated in series, The pumpsfunction to generate sufficient Water pressure and velocity so that thenodules, and other solids, are entrained and are transported by the seawater upwardly through the dredge OPERATION Operation of this equipmentwill now be described, utilizing air-lifting techniques for causingtransport of the mined material.

The surface vessel preferably is equipped with auxiliary equipment andsupplies, to permit operations at a substantial distance from landbases, without the need of direct or continuous land-based support otherthan for transportation of mined materials, food and supplies, andemergency assistance.

When an area of the sea floor, that is to be mined, has beenestablished, a series of at least four taut line buoys is set to a knownand recorded pattern. Each of these buoys is equipped with a sonartransponder, battery powered, with a signaling life of several months.These initial buoys form the master buoys for the area to be mined, andsubsequent mapping and setting of auxiliary marker buoys, of which therewill normally be very many, are related to the original master buoys.The sonar transponders are serviced and repowered, at regular intervalsas needed, by divers.

After an explored area has been staked out, the surface vessel 15 ismoved into operating position. The gathering vehicle or tractor 14 iscarried by the surface A vessel, either on deck, in the center well 61,or suspended directly beneath the center well, when operations arepending.

To begin operations, the tractor 14 is slowly lowered, by adding on theappropriate dredge pipe sections to lengthen the dredge pipesufficiently to lower the tractor to the sea floor. The pendent wireline 21 is held out from the bow of the ship on the boom 122 as thetractor is lowered, and this automatically forms the desired catenary 19at the lower end of the dredge pipe, as the tractor is lowered to thesea floor.

When the final section of dredge pipe has been connected to the shockplunger 62, the entire weight of the dredge pipe is transferred to aspider (not shown) that is mounted at the level of the main deck of thesurface vessel. After the dredge pipe has been secured to the spider,"the receiving tank 111 is placed in position and secured in place foroperations.

The swing joint 85, through which the dredge pipe is connected with thetractor, permits the tractor to move in wide sweeps transversely of thedirection of travel of the surface vessel. This decreases the requiredspeed of the surface vessel, and results in smaller drag forces on thedredge pipe.

The movement of the tractor on the surface of the sea floor is remotelycontrolled from the surface vessel, in order to cause the tractor tomove in a predetermined pattern of movement, or as indicated by thetopography of the sea floor, to skim the surface of the sea floor in theareas traversed. Before the tractor is started on its sweeps over thesea floor, the air lift is placed in operation, to start a current ofsea water up through the dredge pipe.

As the tractor moves over the sea floor, the sea floor is raked toloosen up the material forming the sea floor, and to free up themanganese nodules. The scraper blades 49 and 50 plow all of the nodules,and other solid material, into a bed in the path of the collector head.This bed is immediately traversed by the collector head 91. As thecollector head passes through the bed of nodules and other material fromthe sea floor, the current of sea water passing into the collector headsweeps the bed up, through the screen in the lower face 92 of thecollector head, andthence through the stub pipe and the successivefittings into the dredge pipe.

For efi'icient mining operations, the area to be mined should berelatively flat. When the nodule concentration, of nodules lying on thesurface and within the first six inches of depth of the surface of thesea floor, is about four pounds per square foot of sea floor surface orgreater, strip mining in accordance with the procedure herein describedordinarily is eifective and efficient. The tractor can be driven at aspeed of about one or two feet per second, and the rate of recovery ofnodules may be on the order of to 200 pounds per second, depending uponthe size of the collector head.

For mining manganese nodules at two typical operational depths, thefollowing conditions are recommended for producing satisfactory results:

TABLE 1 [Values are approximate] Water depth, it.

I.D. of dredge pipe, inches 15. 0 l5. 0 Fluid velocity of two phase flow(nodules, other solids, and sea water), in the bottom portion of dredgepipe, fiL/see 17. 1 17. 1 Maximum elocity of nodules in two phase floftJsec 14. 4 14. 4 Minimum velocity of nodules in two phase flow,

ft./sec 7.7 7.7 Average probable velocity of nodules in three phase flow(solids including nodules, sea water, and air),

ft./sec 73 73 Distance of air injection below surface of water,

It 1, 375 2, Percent of water depth to point of air injection 23 18Injection air pressure to start system (gauge), lbs./

Volume of air-quantity, c.r.m 10, 600 16, 000 Compressor horsepower tomaintain system 1, 800 3, 400 Compressor horsepower total on dredge 4,000 8, 000 Total flow (slurry), lbs. min 87, 300 87, 300 Total flow(nodules), lbs/min 9, 000 9, 000

As indicated in the foregoing table, in order to start the initialupward flow of sea water through the dredge pipe, it is necessary to useair that is in excess of the static head of the water at the injectionpoint, so as to start a pumping effect from the injected air. However,after the water is in motion, the pressure of the air can be loweredconsiderably to a maintenance level that is still sufficient to keep thefluid in motion. At the collector head, the inward rush of sea watersweeps the nodules and other loose material, that have been formed intoa bed by the scraper blades, into the collector head and up the dredgepipe.

At the upper end of the dredge pipe, the material discharges into thechamber of the tank 111. This chamber is maintained at asuperatmospheric pressure, such as, for example, about 22 p.s.i.g. orhigher. The solids portion of the three phase mixture, that isdischarged into the tank 111, settles rapidly. The solids aretransferred through the rotary valve 116 from the bottom of the tankinto a material handling system, such as, for example, a transferconveyor, that will transfer the solid materials into appropriatehoppers. The sea water is allowed to run off and return directly to thesea.

The figures for nodule recovery are based upon nodules having a largestdimension of about 8", about 0.6 sphericity, specific gravity 2.1, anddensity of about 131 lbs/cu. ft.

For operating at a 6,000 foot depth, the air injection site preferablyis located about 1,375 feet below the surface of the sea, and at theoperating injection pressure of 9 355 p.s.i.a., the daily air rate isabout 15.4 std. MCF. Preferably, the compressors withdraw air from thetank 111 into which the dredge pipe discharges. This air is thencompressed and returned to the dredge pipe at the injection site.

As a design precaution, it is preferred that the compressed air systemby flexible, with multiple compressor units, with at least 100 percentof standby capacity, and reserve high pressure air tanks, all capable ofdelivering compressed air in a wide range of pressure.

For mining in water depths of up to about 12,000 feet, an exemplarydredge pipe string would be constituted as follows, from the sea floorup:

To minimize the power required for operations, it is preferred that theair injection site be located at a depth of at least 1,000 feet blow thesurface of the sea.

When hydraulic lifting is employed rather than air lifting, centrifugalpumps replace the air injection system, and the dredge pipe dischargesdirectly into the atmosphere instead of into a pressurized dischargechamber. For mining operations down to about 6,000 feet of water, it ispreferred to employ two pumps of 1500 HP. each, operating in series,located about 600 feet below the surface of the sea. These pumps shouldbe constant speed, A.C. powered pumps, with adequate motors to meetmaximum emergency power fluctuations. For mining operations at depths onthe order of 12,000 feet, it is preferred to employ four pumps,operating in series and located about 1,000 feet below the surface ofthe sea.

OTHER FACTORS In the event of damage to the dredge pipe or tractor, orafter exhaustion of a particular mining area, the dredge pipe andtractor can be hauled aboard the surface vessel, as indicatedschematically in FIGURE 11. In the event that a storm requires that thesurface vessel abandon a particular area quickly, the dredge pipe can bedisconnected from the surface vessel, but left connected to the buoy 22through the pendent line 21, and the dredge pipe can simply be laid onthe sea floor, for retrieval after the storm.

Preferably, a sonar transponder or repeating target is mounted adjacentpreselected joints, at intervals along the length of the dredge pipe,and, as well, on the gathering vehicle. These units will respond to theultrasonic sound of a sonar transmitter on the surface vessel, and theirtransmitted energy will in turn be received on the ship. By a suitabledisplay of these signals in both plan and elevation, the configurationof the pipe line, and the location of the gathering vehicle relative tothe surface vessel, are ascertained.

All of the electric power supply that is required to drive the bottomvehicle and control it, for the underwater television equipment andflood lights, and for the instruments, preferably is supplied in onecomposite cable. This power supply cable is attached to each section ofthe dredge pipe by means of a suitable quick-connecting clamp. Forconvenience, cable reels are mounted on the deck of the surface vessel,for stowing and reeling out of the cable. The cable preferably isprepared in lengths of approximately 6,000 feet, with watertightconnectors at the joints. Amplifiers for the underwater television areinserted in these joints, as needed.

The composite cable is made up of individual wires as needed for power,lights, electronics and controls, all suitably assembled in one unit andthen covered with a moisture-impermeable insulation, protected by doublearmor, reverse lay wrapping. The end of the cable is let out of thecenter axle of the cable reel, and is terminated in suitable connectorsthat are connected up for operation after the vehicle is in operativeposition on the sea floor.

While the invention has been disclosed herein by reference to thedetails of preferred embodiments thereof, it is to be understood thatsuch disclosure is intended in an illustrative, rather than in alimiting sense, and it is contemplated that various modifications in theconstruction and arrangement of the various parts of the equipmentdescribed herein will readily occur to those skilled in this art, allwithin the spirit of the invention.

What is claimed is:

1. A device for skimming and collecting deposits from the sea floor,comprising:

tractor means for movement over the sea floor, including drive meansdisposed at opposite sides of said tractor for supporting and drivingsaid tractor on the sea floor;

a dredge pipe for transporting collected deposits;

a collector head that is mounted on said tractor intermediate said drivemeans and remote from the leading end and rearward of said leading endof the tractor and said collector head having openings on a face thereofopening toward the leading end of said tractor and disposed to receivedeposits from the sea floor;

means interconnecting and providing communication between said collectorhead and said dredge pipe, and

a pair of scraper blades that are mounted intermediate said drive means,for movement upon movement of said tractor, and that are disposed forskimming the sea floor and that converge together toward said collectorhead, to direct skimmed deposits toward the collector head, butterminating forwardly of said collector head to provide an outlet forsaid deposits, said collector head inlet openings being disposedopposite said scraper blade outlet.

2. A device in accordance with claim 1 wherein said interconnectingmeans is formed to permit horizontal and vertical movement of saiddredge pipe relative to said tractor.

3. A device in accordance with claim 1, wherein said collector head isformed with a free, trailing end that is disposed for sliding movementover obstructions on the sea floor, and is also formed with a collectingopening in advance of its free end in the direction of movement of thetractor, said collecting opening being disposed to confront the skimmeddeposits and wherein said collector head is mounted on said tractor forpivotal movement about a generally horizontal axis thereon.

4. Means for mining deposits from the sea floor, comprising, incombination:

a surface vessel;

tractor means for movement over the sea floor, including drive meansdisposed at opposite sides of said tractor for supporting and drivingsaid tractor on the sea floor;

a dredge pipe for transporting collected deposits;

a collector head that is mounted on said tractor intermediate said drivemeans and remote from the leading end and rearward of said leading endof the tractor and said collector head having openings on a face thereofopening toward the leading end of said tractor and disposed to receivedeposits from the sea floor;

means interconnecting and providing communication between said collectorhead and said dredge pipe, and

a pair of scraper blades that are mounted intermediate said drive means,for movement upon movement of said tractor, and that are disposed forskimming the sea floor and that converge together toward said collectorhead, to direct skimmed deposits toward the collector head, butterminating forwardly of said collector head to provide an outlet forsaid deposits, said collector head inlet openings being disposedopposite said Scrapper blade outlet; and means communicating with saiddredge pipe intermediate said vehicle and said vessel, for effectingtransport of said gathered deposits through said pipe.

5. .Mining means in accordance with claim 4 wherein the collector headgathers a mixture of said deposits and a volume of sea water to serve asa carrier medium for transporting the deposits and wherein a forcegenerating means is used for generating within said dredge pipe, at alocation intermediate its ends, a sufiicient lifting force to cause acontinuous flow of said mixture of sea water and deposits upwardlythrough said pipe.

6. Mining means in accordance with claim 5 wherein said force generatingmeans comprises means for injecting compressed air into the mixture ofsea water and deposits.

7. Mining means in accordance with claim 5 wherein said dredge pipe issuspended at its upper end from said vessel and wherein said pipe isarticulated for flexibility.

8. Mining means in accordance with claim 5, including buoyancy meanssecured to said dredge pipe intermediate its ends, to support asubstantial portion of the pipe weight below said buoyancy means, and torelieve said means interconnecting said collector head and said dredgepipe of substantially all stress attributable to the weight of thedredge pipe thereabove.

9. Means for mining deposits for the sea floor, comprising, incombination:

a surface vessel;

a self-propelled gathering vehicle for movement over the sea floor;

collector means mounted on said vehicle, for gathering therein a mixtureof said deposits from the sea floor and a volume of sea Water to serveas a carrier medium for transporting the deposits;

an articulated dredge pipe that communicates with said collector means,for delivering said mixture from said vehicle to said vessel;

air compressor means mounted on said vessel;

auxiliary pipe means secured to said dredge pipe at least along an upperportion of the length of the dredge pipe, and communicating with saiddredge pipe at least at one location intermediate said vehicle and saidvessel, to provide communication between said compressor and said dredgepipe, for injecting compressed air into said dredge pipe to effecttransport of said mixture of sea water and deposits upwardly throughsaid dredge pipe;

a tank mounted on said vessel;

means for maintaining said tank under superatmospheric pressure;

said dredge pipe being disposed to discharge into said tank under theambient pressure of the tank; and means permitting the discharge of thesea water and of the gathered deposits from the tank into theatmosphere, while permitting the maintenance of superatmosphericpressure in the tank.

10. Means for mining nodular deposits from the sea floor, comprising, incombination:

a surface vessel;

a self-propelled gathering vehicle comprising tractor means for movementover the sea floor, under remote control from the surface vessel;

an articulated sectional dredge pipe for delivering gathered depositsfrom said tractor to said vessel, said dredge pipe being supported atits upper end from said vessel, and said dredge pipe being disposed inthe form of a catenary adjacent its lower end, and with a plurality ofball joints intermediate dredge pipe sections respectively along thelength of the catenary;

means supporting at least a substantial part of the 12' weight of theunderlying portion of the dredge pipe at at least one location beneaththe surface vessel and intermediate the ends of the dredge pipe;

a collector head that is mounted on said tractor and that is disposedfor gathering therein a mixture of said deposits and a volume of seawater to serve as a carrier medium for transporting the deposits, saidcollector head being mounted on said tractor for pivotal movement abouta generally horizontal axis thereon, with a free end thereof formed anddisposed for sliding movement over obstructions on the sea floor, andwherein said collector head is formed with a collecting opening ahead ofits free end in the direction of movement of the tractor, saidcollecting opening being disposed to confront the gathered deposits;

means mounted for movement upon movement of said tractor, and disposedto gather deposits and direct them toward said collector head;

means interconnecting and providing communication between said collectorhead and the lower end of said dredge pipe, said interconnecting meansbeing formed to permit horizontal and vertical movement of said dredgepipe relative to said tractor and said,

collector head; and

means for generating within said pipe, at a location intermediate saidtractor and said vessel, a sufiicient lifting force to cause acontinuous flow of said mixture of sea water and of said gathereddeposits through said dredge pipe up to said vessel.

11. A process for mining deposits on the sea floor,

comprising:

skimming the sea floor;

mixing the skimmed material with a suflicient volume of sea water toserve as a carrier;

delivering the mixture to a dredge pipe;

injecting compressed air into the dredge pipe at least at one locationintermediate the ends of the dredge pipe and at a substantial distancebelow the surface of the sea, to create a pressure differential in thedredge pipe to cause an upward flow of the mixture therethrough; and

discharging the dredge pipe into a chamber under superatmosphericpressure to collect the skimmed material.

References Cited UNITED STATES PATENTS 1,997,149 4/1935 Lake.

216,686 6/1879 Lewis 37-59 523,838 7/1894 Hussey 37-59 692,815 2/1902Bates 37-63 1,415,113 5/1922 Phillips 37-61 XR 1,556,128 10/1925 Roos3'7-195 XR 2,826,836 3/1958 Hofiman 37-58 3,226,854 1/1966 Mero 37-583,286,286 11/1966 Nelson 37-72 XR FOREIGN PATENTS 939,644 10/1963 GreatBritain.

8/ 1964 Canada. 9/1951 France.

OTHER REFERENCES Engineering Aspects of Mineral Recovery From the OceanFloor by George S. Lockwood. Mining Engineering, August 1964, pp. 45-49.(Referred to as the Lockwood article.)

ANTONIO F. GUIDA, Primary Examiner A. E. KOPECKI, Assistant ExaminerU.S. Cl. X.R. 172-777

